Unlike protein and fat, carbohydrates are not essential to human life.

The body can produce glucose from protein and fat, however carbohydrates are the most convenient and quickest way for the body to produce energy.

Some weight-loss diets exclude or reduce carbohydrate intake triggering the body to convert its supply of fat to glucose.

There are two types of carbohydrates, simple and complex:

Simple Carbohydrates

Simple carbohydrates refer to sugars with a simple molecular construction of one or two parts.

Because of their simple molecular structure the body can process these simple sugars quickly – this leads to an energy spike, a sudden rush of energy as sugars are converted to glucose followed by a low once the process is complete and the simple carbohydrates have been used.

Processed and refined sugars tend to have a high Glycaemic Index (GI) – affecting blood sugar levels quickly - compared to naturally occurring complex carbohydrates which in turn have a lower GI.

Refined sugar is a common source of simple carbohydrates in the modern diet.

Many processed, packaged and fast foods contain simple carbohydrates as ‘sugar’ is used as a flavour enhancer and can satisfy our palates for sweet food. Simple carbohydrates from added sugar have little or no nutritional value and are often described as ‘empty calories’. Most people can benefit from reducing their intake of added sugar (simple carbohydrates). If you buy processed and packaged foods, choose those with less added sugar, reduce consumption of sugary foods such as cakes, biscuits (cookies), sweets (candy) and regular (not diet) soft drinks.

Simple carbohydrates are not always bad and also exist naturally in foods that do provide nutritional benefits, notably fruits, milk and other dairy products. Most fruits contain good levels of fibre, vitamins and micro minerals as well as antioxidants. Milk and dairy products are good sources of protein and calcium, most people agree that both fruit and dairy products are important to a well-balanced healthy diet.

Complex Carbohydrates

Complex carbohydrates refer to sugars with a complex molecular structure of three or more parts; due to the complex structure of these molecules it takes the body longer to break them down to produce the glucose it needs for energy. Foods rich in complex carbohydrates also contain valuable vitamins, minerals and fibre which are vital to overall health and wellbeing.

As foods containing complex carbohydrates are processed more slowly by the body they can provide sustained energy levels over longer periods of time than simple carbohydrates. The Glycaemic Index (GI) of foods rich in complex carbohydrates is therefore lower.

Consuming too many carbohydrates or the wrong type of carbohydrate can upset the balance of your body's blood sugar levels. This can result in energy highs and lows and mood swings - which, in turn, can leave you feeling tired and irritated.

If you often feel tired after lunch try eating more protein and vegetables but less carbohydrates and avoid alcohol.

Glycaemic Index (GI)

The glycaemic index of food is a measure of how quickly glucose levels rise in the blood after eating. Foods with higher GI levels tend to contain more simple carbohydrates whereas foods containing complex carbohydrates will tend to produce a lower GI score as it takes the body longer to break these down into glucose.

Generally foods with a lower GI, which release glucose more slowly, are considered healthier – because the body has to work harder to break these foods down you feel fuller for longer and burn more calories digesting and recovering glucose. However, some foods with lower GI scores are also high in fat and salt which may make them less healthy.

Example GI scores:

White Bread – 71

Wholemeal Bread – 49

Steamed White Rice – 98

Basmati Rice – 58

Chocolate (Milk) - 49

Whole Milk - 27

Skimmed Milk - 32

Dry Roasted Peanuts - 14

How Much Carbohydrate Do We Need?

There is no simple answer to this question and different people have different ideas about carbohydrate consumption. However, as a general rule we should aim to get approximately half of our energy from carbohydrates, ideally 90% of this coming from complex carbohydrates and only 10% from refined and processed sugars, (simple carbohydrates).

A simple way to achieve a healthy well-balanced diet is to eat a variety of foods during the day. Some people recommend that at each meal a plate should be split so that a quarter is high protein food, meat, fish, eggs, dairy produce etc (see our page What is Protein? for more information). A quarter of the plate is high carbohydrate food, potatoes, pasta, rice, bread, beans. The rest of the plate (half) should be made up of fresh vegetables, which will provide carbohydrates and protein in lower levels but also many vitamins and minerals. Finish your meal with a piece of fruit which will provide you with all the simple carbohydrates you need.

What if I Eat Too Many Carbohydrates?

Eating too many carbohydrates will lead to weight gain, this is because the body will store unused glucose for later use.

Usually, however, it is how the carbohydrates are prepared which will have the greatest effect on weight gain. Although chocolate and apples both have simple carbohydrates, chocolate also contains fat – an apple on the other hand contains fibre, vitamins and minerals. French fries, chips, crisps and roast potatoes are all prepared using fat and therefore contain fat – baked and boiled potatoes are better for you as they have not been prepared in fat. Similarly, steamed rice is much better than fried rice and bread is better for you without adding butter or margarine.

In Summary

Carbohydrates contain the glucose that the body needs for energy. There are two main types of carbohydrates, simple and complex. The more refined the carbohydrate the more quickly it is converted to glucose and released into the bloodstream. This can cause peaks and troughs in blood sugar levels and results in variable energy levels – refined or simple carbohydrates should make up only about 10% of your daily carbohydrate intake.

Complex carbohydrates, such as those found in starchy foods such as potatoes, bread, rice, whole grains, pasta and oats release glucose more slowly into the bloodstream providing more stable and sustainable energy levels to the body.

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